Foam stability refers to the absence of issues such as foam rupture, closed cells, or collapse, while also ensuring that properties like hardness, density, elasticity, tensile strength, and cell structure meet customer specifications. Achieving this requires standardizing raw materials, formulations, and operating parameters to control complex chemical reactions across varying environmental conditions.
Density is measured in kilograms per cubic meter (kg/m³) or grams per cubic centimeter (g/cm³). It is determined by the formulation and influenced by the reaction rate.
There are two types of foam hardness: surface hardness (relevant for footwear-grade foam) and overall hardness (relevant for furniture-grade foam). Foam hardness is linked to "hard segments" formed during the reaction, heat generation, and the solids content of raw materials-specifically TDI, MC, and POP. It is also influenced by the degree of cross-linking.
Elasticity depends primarily on the molecular weight of the polyether; higher molecular weight results in higher resilience. It is also influenced by the extent of branching during the reaction-fewer branches generally yield better elasticity.
Furniture-grade foam is primarily used for seating and backrests. Tensile strength is related to the quantity of NCO groups and the degree of cross-linking. Increasing the TDI index or the internal heat of the foam enhances both NCO content and cross-linking. Conversely, increasing MC lowers the internal temperature, which often hinders the development of tensile strength.
Foam with high-quality cell structure is typically classified as mid-to-high-end product. Achieving a uniform, fine, and defect-free cell structure is a complex challenge that requires a deep understanding of the machinery, raw materials, formulations, and processing parameters.
